Mertesacker says it like it is

"The best team went through. Monaco deserved it because they played much better in the first leg. We played well today but it was a massive deficit, and it wasn't enough tonight. We came here and tried absolutely everything, and when you look at the game we could have scored more than two.
"Monaco deserve it and that's absolutely fine. They caused a lot of problems away from home. We have to admit that we regret the first game.
"But if we continue to play like that we'll do well in the FA Cup and the league. But play as badly as we did in the first game and you're out of the Champions League. Monaco deserved it."